What is the minimum degree of trunk flexion to optimally activate the rectus abdominis during a curl-up on a physioball?

The optimal degree of trunk flexion to effectively activate the rectus abdominis during a curl-up on a physioball is around 30 degrees. This angle strikes a balance that allows for sufficient engagement of the muscle without risking strain on the lower back or compromising form.

At 30 degrees of flexion, the rectus abdominis is appropriately engaged as it begins to contract, facilitating its action without necessitating excessive flexion, which could lead to diminished activation or potential injury. As the trunk continues to flex beyond this point, other muscles may take over the workload, leading to less effective targeting of the rectus abdominis. Therefore, training at this angle promotes both safety and effectiveness in abdominal strengthening exercises on the physioball.